This invention relates to the extrusion of moldable material into pellets or cubes, and more particularly to an extrusion die for use in such connection. The effective length and diameter of a die hole is a carefully selected balance between capacity and pellet quality and wear and strength of the die. A short effective length usually increases capacity and lowers power consumption, whereas a thicker die promotes solid pellet formation at the expense of power and capacity. A larger effective diameter generally promotes capacity at the expense of pellet quality.
It is an object of this invention to produce a die which improves the quality of the pellet without decreasing capacity. It is also an object to provide a stronger die without substantial cost increase.
It is a further object of this invention to provide a pellet die hole which has a smooth inlet portion wherein the pellet is formed, and a ridged or rippled outlet portion wherein the diameter of the formed pellet is retained under controlled conditions which reduce friction and minimize heat transfer from the pellet.
These and other objects are obtained in a pellet mill die construction comprising a die member having a multiplicity of die holes constituting extrusion passages extending between the inner and outer faces thereof, each of the die holes comprising a bore hole having a smooth internal bore extending from the inner face at least part way through the die hole, and a ridged internal bore of equal effective diameter extending from the smooth bore towards the outer face.